1. Field of the Invention
The invention is directed to a prosthetic foot which is able to absorb the shocks developed during ambulation with efficient energy transfer between heel strike and toe-off, and to enhance stability.
2. Descrption of the Related Art
Specialized prosthetic feet have recently been developed in an effort to satisfy the specialized needs of different amputees. For example, active amputees who engage in sports or other strenuous physical activities typically require a prosthetic foot which is capable of both absorbing energy during a heel strike of each step, of efficiently transferring the energy to the toe of the prosthesis as the step progresses, and of releasing the stored energy at the moment of toe-off to provide energy for the next step.
In particular, during ambulation the foot initially contacts the ground at the heel. During strenuous activities, it is desirable for a prosthesis to be able to absorb the shock of this heel strike, and to transfer the absorbed energy to the toe portion of the prosthetic foot for release upon the subsequent toe-off so that the rebound energy is maximized. An effort to design a prosthetic foot capable of storing and subsequently releasing energy during ambulation is disclosed in U.S. Pat. No. 5,458,656 in which the pylon is formed of two telescoping parts connected by a spring. An upper part of the pylon incorporates a top adapter for connection to the residual stump of the wearer while the bottom part supports heel and toe springs. The energy of a heel strike is absorbed by the spring during telescoping of the pylon and is intended to be released as the load is removed from the prosthesis during toe-off.
However, this conventional design has a number of problems. The telescoping pylon tends to bind due to turning moments applied from the toe as the user""s weight is shifted to the toe of the prosthesis. Since the telescoping pylon is designed to compress at heel strike while the toe spring is designed to flex between mid-stance and toe off, and the heel lever arm is much shorter than the toe lever arm, the stiffness of the telescoping pylon is typically less than the stiffness of the toe spring. For these reasons and because the toe spring is supported by the telescoping pylon, the pylon tends to remain compressed until after toe off, and so the energy of the heel strike is not efficiently transferred to the toe spring for use during toe-off. Since the toe spring and the telescoping pylon are acting in series when the toe is loaded, the telescoping pylon can dampen the energy return response of the toe spring, making the device less dynamic than desired. Also, since the toe portion of the prosthesis is mounted exclusively to the telescoping pylon, the height of the prosthesis may be excessive, and the apparent length of the user""s leg will vary markedly during walkingxe2x80x94an unnatural and undesirable tell-tale of the presence of the prosthesis.
It is an object of the present invention to provide a prosthetic foot which can absorb energy on heel strike and efficiently transfer the energy to the toe of the prosthesis for use during toe-off.
It is a further object of the invention to provide a prosthetic foot with enhanced stability, control, function and durability.
It is yet a further object of the invention to provide a prosthetic foot which is not subject to the shortcomings of the prior art.
According to a feature of the invention, a prosthetic foot includes an adapter element securable to a residual limb, a foot plate having a heel portion and a toe portion along the length thereof, at least one toe spring connected between the adapter element and the toe portion of the foot plate, and a heel spring connected between the adapter element and the heel portion.
Since the toe spring of the prosthetic foot according to this feature of the invention is connected between the foot plate and to the adapter element, it can efficiently transfer energy to the toe portion during toe-off.
According to a further feature of the invention, a prosthetic foot comprises an adapter element securable to a residual limb, a foot plate having a heel portion and a toe portion along the length thereof, and at least one toe spring connected between the adapter element and the toe portion of the foot plate, the toe spring comprising a curved leaf spring whose concave side exhibits a plurality of transverse ribs.
According to this feature of the invention, the transverse ribs create a more constant stress spring, and effectively distribute the bending stresses along the length of the spring. This minimizes the risk of delamination of the toe spring and permits more efficient energy transfer during toe-off.
According to yet a further feature of the invention, a prosthetic foot comprises a tubular pylon having one end securable to a residual limb, a collar mounted to the pylon for movement along the length of the pylon, a toe spring extending from the collar, a heel spring extending from the collar such that the toe and heel springs comprise toe and heel portions of the prosthetic foot, a further heel spring connected between the heel portion and another end of the pylon, and a non-extensible band extending between the heel portion and the collar.
The further heel spring according to this feature of the invention reduces loading at the socket of the prosthesis, and the non-extensible band limits the movement of the collar away from the heel during the rebound of the heel spring, and thereby promotes efficient energy transfer to the toe spring for release during toe-off.
According to yet a further feature of the invention, a prosthetic foot comprises a tubular pylon having one end securable to a residual limb, a foot plate having a heel portion and a toe portion along the length thereof, a collar mounted to the pylon for movement along the length of the pylon, at least one toe spring connected between the collar and the toe portion of the foot plate, and a heel spring connected between the heel portion and another end of the pylon.
According to yet a further feature of the invention, a prosthetic foot comprises elements made from layers of precured composite sheets bonded together with adhesives.